The SCE or DC was defined in 3GPP (3rd Generation Partnership Project) RAN (Radio Access Network) working groups, and it has initiated a study on security aspect and impact on the architecture 1A defined in NPL 1.
An UE (User Equipment) in DC is connected to both MeNB (Master eNB (evolved Node B)) and SeNB (Secondary eNB). Since there is only one S1-MME connection in the DC architecture which is between MeNB and MME (Mobility Management Entity), the handover means handover of MeNB. When a handover happens, it was agreed that SeNB should be torn down first as disclosed in NPLs 2 to 4.